Dosing and sealing of fluid-based electro-optical devices and displays

ABSTRACT

A method for manufacturing an electrofluidic device comprising the steps of providing a first plate with features for holding a first fluid, filling a first fluid into features on a first plate; providing a second plate and sealing a second plate onto the first plate forming stacked plates with at least one cavity between the plates, and leaving at least one fill port for a second fluid. Thereafter, the stacked plates are cooled to increase the viscosity of the first fluid so that the first fluid maintains a fixed position as a second fluid is filled into the cavity. Methods are disclosed.

RELATED APPLICATION

The Present application claims priority to U.S. Ser. No. 61/979,207filed Apr. 14, 2014, the disclosure of which is hereby incorporatedherein by reference in its entirety.

GOVERNMENT RIGHTS

This invention may have been made with government support undercontracts 1058302 and 1 127463 awarded by the National ScienceFoundation. The government may have certain rights in the invention.

BACKGROUND OF THE INVENTION

Reflective displays are commercially important in product areas thatinclude electronic readers (e-Readers) and electronic shelf labels.However, current reflective displays lack the performance of colorprinting on paper. Electrofluidic displays (EFDs), which were introducedin 2009, can provide vivid color, high brightness, and fast switching ina reflective display. Due to its unbeatable color performance,electrofluidic displays provide a solution for future e-papertechnology. But due to its specific pixel structure and two differentfluids, electrofluidic displays need a novel dosing and sealingtechnology.

Liquid crystal displays (LCDs) incorporate assemblies that are filledwith only a single fluid - a liquid crystal fluid. Traditionally, theliquid crystal fluid has been filled into a LCD by first creating acavity assembly between two plates, where the perimeter of the plates issealed with the exception of providing a fill port. The structure isthen subjected to vacuum to remove gases from the cavity assembly andthereafter dipped in a liquid crystal pool to allow liquid crystal tooccupy the cavities between the plates. In addition, the plates may besubjected to a pressurized environment to drive liquid crystal into thecavities.

With extreme demand for the large LCD panels, this industry startedusing vacuum based ‘drop’ fill processes. In a drop fill liquid crystalprocess, drops of liquid crystal are placed upon a first plate (bottomplate) in vacuum at a precisely measured volume, and then a second plate(top plate) is positioned and bonded to the first plate to sandwich thecavity assembly therebetween, all in vacuum.

LCDs may be fabricated using liquid filling, but LCDs do not utilize twoimmiscible fluids and fail to address any of the problems associatedwith moving a first fluid (polar or nonpolar) over a second fluid(opposite of the first fluid) without displacing it. LCDs purposelyavoid low temperature because the liquid crystal becomes too viscous tofill (fill time increased exponentially with decreasing temperature).Accordingly, these LCD processes cannot be adapted for EFDs.

In contrast to LCDs, EFDs and electrowetting displays (EWDs) require atleast two immiscible fluids. During device fabrication, these twofluids, one being polar, and one being non-polar, must be loaded into adisplay module and then the display module is sealed. The surface energyof the materials, combined with the surface energy of the coatings inthe display structure, the properties of the sealant, and the need toomit air bubbles from the display pose a significant technicalchallenge.

For EWDs, multiple dosing technologies have been reported. Researchersfrom University of Cincinnati reported self-assembled oil dosingtechnique utilizing the low surface tension of a colored nonpolar fluid.For this oil dosing process, the device is submerged into a polar fluid,and then a colored nonpolar fluid is injected by needles and then filledinto pixels resulting from surface tension. Likewise, an ink-jetprinting technique has been demonstrated to inject a colored nonpolarfluid into pixels on one plate, followed by covering the nonpolar fluidwith a transparent polar fluid and capping the assembly with a topplate. Accordingly, EWD dosing processes always result in the colorednonpolar fluid filling a microwell. But, for EFDs, just the opposite isthe case—a polar fluid must fill the microwell. Moreover, LCDs and EWDsdo not involve filling cavities having a dimension in the range of tensof micrometers with individual fluids bodies, and consequently do notencounter air entrapment in small cavities, cleaving the fluid body tokeep the ink in the cavities, or enhanced evaporation of the fluid dueto its small radius of curvature.

Consequently, there is a need in the art for dosing techniquesapplicable to EFDs that provides for a reasonable cost display orshutter. More specifically, there is a need for dosing and sealingtechnologies that provide a reasonable cost manufacturing method forfabricating displays with two liquids inside, wherein one liquid isspecifically placed into features, and no air is trapped in the device.

The invention will be further appreciated in light of the followingdetailed description and drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C depict a sequential process for ink filling ofelectrofluidic devices.

FIGS. 2A-2C depict a sequential process for forming fluid cavitieswithin electrofluidic devices.

FIGS. 3A-3C depict a sequential process for filling fluid cavitieswithin electrofluidic devices with oil.

FIG. 4 depicts an exemplary pressurization process carried out onelectrofluidic devices subsequent to filling of polar (ink) and nonpolar(oil) fluids.

FIGS. 5A-5B depict an exemplary ink application process carried out onelectrofluidic devices.

FIGS. 6A-6C depict an exemplary sequence in accordance with the instantdisclosure.

FIGS. 7A-7C depict an exemplary sequence in accordance with the instantdisclosure.

FIGS. 8A-8C depict an exemplary sequence in accordance with the instantdisclosure.

FIGS. 9A-9C depict an exemplary sequence in accordance with the instantdisclosure.

FIGS. 10A-10C depict an exemplary sequence in accordance with theinstant disclosure.

FIGS. 11A-11C depict an exemplary sequence in accordance with theinstant disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Although the present disclosure will be described in connection withcertain embodiments, the description of one or more embodiments is notintended to cover all alternatives, modifications, and equivalentarrangements as may be included within the spirit of the presentdisclosure. In particular, those of ordinary skill in the art willrecognize that the components of the various electrofluidic devicesdescribed herein may be arranged in multiple different ways.

Several novel methods are disclosed for successfully incorporatingmultiple fluids into electrofluidic devices while meeting devicecompatibility and performance requirements. Electrofluidic devices anddisplays operate by moving the relative position of a polar fluid and anon-polar fluid. The polar fluid is typically a mixture that contains amajority of a polar solvent, non-limiting examples of which includewater, ethylene glycol, propylene glycol, gamma butyrolactone, andpropylene carbonate. The non-polar fluid is typically a hydrocarbon orsilicone-based oil. In a typical electrofluidic device, a colorant isadded to the polar phase, such as a pigment or a dye. Colorants may alsobe added to the oil. Electrowetting displays typically dose thenon-polar fluid onto the plate with fluid-holding features first, andpolar phase second. Electrofluidic displays typically dose the polarfluid onto the plate with fluid-holding features first, and thenon-polar phase second.

Electrofluidic and electrowetting devices are fabricated from a startingsubstrate, or first plate. Surface features and electronic film layersare incorporated on the first plate. The plate itself can be eitherrigid (i.e. a sheet of glass), or flexible (i.e. a sheet of plastic), ora sheet of flexible material bonded to a sheet of rigid material forsupport. The surface features, for example, can be array of pixelstructures comprising a central well or hole in a surface to store afirst fluid, surrounded by a wall structure to contain this fluid duringelectrical actuation, as described in U.S. Pat. No. 8,111,465. Likewise,a top plate, forming a cavity for fluids, can also be a rigid sheet, aflexible sheet, or a combination of the two.

In example 1, the problem of dosing the two fluids while eliminating airbubbles is solved by following a first exemplary process. In step 1, asshown in FIG. 1A, a first plate 10 with surface features is positionedin a vacuum chamber 12 and vacuum is pulled to remove gases pulling avacuum to remove air from the cavities. Referring to FIGS. 1A and 1B,the vacuum chamber 12 may include an ink supply 14 (i.e., an ink bath)in order to immerse the substrate 10 in the ink supply 14 after vacuumhas been pulled for a predetermined period of time. After the substrate10 is immersed in the ink supply 14, and while the substrate 10 remainsimmersed in the ink supply 14, the pressure is increased to push the inkinto the wells. An example pressure increase is obtained by ventingvacuum chamber 12 is vented to allow atmospheric conditions. Butpressures above 50 torr will provide this benefit for certainconditions. After the vacuum chamber 12 is vented, as shown in FIG. 1C,the substrate 10 is removed from the ink supply 14 and the ink isremoved from the surface of the substrate 10. More specifically, theremoval of ink cleaves the ink on the surface and it remains in thecavities. It should be noted that the ink supply 14 within the vacuumchamber 12, in addition to the substrate 10 with the ink after cleaving,is chilled to reduce its evaporation rate of the ink.

Referring to FIG. 2A, in step 2, an adhesive 16 (e.g., a UV-curableadhesive) is applied to a top plate 18. As shown in FIG. 2B, the topplate with adhesive 16 is aligned (with the aid of cameras 19) andcontacts the substrate plate 10. Pressure is then applied, as shown inFIG. 2C, to the plate stack 20 while the adhesive 16 is UV-cured tocreate cavities between the top plate 18 and substrate 10 that will befilled with a second fluid (oil) in a following step. It should be notedthat the adhesive pattern leaves at least one open port 22 for eachdisplay that allows filling of the second fluid.

Referencing FIG. 3A, the plate stack 20, which forms a single module, isplaced into a vacuum chamber 12 and the pressure is reduced to removegases from the cavities. The plate stack 20 may be pre-chilled prior tobe placed into vacuum to reduce evaporation of the ink solvent. As shownin FIG. 3B, the plate stack 20 is thereafter immersed into a volume ofoil (i.e., and oil bath) under vacuum while the temperature of the platestack 20 is at or near the freezing point of the ink (first fluid). Inone embodiment, the oil is chilled to −65° C. The part is immersed to alevel below the fill port 22. Once the ink has become more chilled, thepressure can be reduced still further. An exemplary value of pressure isless than 10 torr, and preferably less than 1 torr. Next the plate stack20 is fully immersed into the oil to allow the open port 22 for eachdisplay to accept oil into the cavities. As shown in FIG. 3C, to furtherdrive the oil into the channel, the pressure in the chamber isincreased. An example increase would be to raise the pressure to 650torr. The oil does not displace the chilled ink, which provides auniform filling. Lack of clamping pressure during the oil dosing stepfacilitates the oil filling the cavities between the spacers and the topplate. The gap can be sufficient to fill completely closed pixels cells.After filling, the stack 20 is removed from the oil supply 24.

Referring to FIG. 4, the plate stack 20, which is also a single module,is placed under pressure to push the top plate against the substrate.Suitable means of applying pressure include an air bladder device 26.Multiple modules (or plate stacks) may be positioned on top of oneanother forming a stack of modules 28, and collectively pressurized sothat pressure is applied between the first module and last module of thestack of modules 28. The pressure, exemplary values ranging from 3 psigto 15 psig, sets the proper cell gap and can be used to adjust thetension in the stack of modules 28 after the final seal. With pressureapplied, excess oil is cleaned from the fill port 22 and a second amountof adhesive is applied and cured to seal the fill port 22.

The choice of the ink/oil combination is very important. There are manycompeting design constraints. First, the ink and oil need to operate ator below −20° C. and survive −40° C. for typical applications, so theymust both have freezing points below −40° C. and viscosities below 500cp at −20° C. Next, for the assembly process described in example 1, theink must have a freezing point significantly higher in temperature thanthe oil so that the viscosities of the two fluids differ by orders ofmagnitude at the oil fill temperature. The viscosity of the ink mustremain low enough at the oil fill temperature so that it does not getdisplaced from the wells. In addition, the ink must be insoluble in theoil. This can be measured by placing a small (1 pL) drop of ink into alarge (20 mL) volume of oil, and measuring the volume of the drop overtime. If the drop decreases by less than 5% over 24 hours, the diffusionis small enough for the application. Also, the electrowettingperformance must be suitable (must have a Young's angle ≧160° andelectrowet down to ≦65°. Finally the interfacial tension between thepolar and non-polar phases must be sufficiently high to prevent dropletejection or splitting in the electrofluidic channel (>9 mN/m). Examplepolar fluids and mixtures include: ethylene glycol, propylene glycol,glycerol, gamma butryolactone, and propylene carbonate. Examplenon-polar fluids include butyl cyclohexane, butyl cycloheptane, isoparM, isopar K, and isopar V.

In the case of an electrowetting display, the ink and oil phases arereversed from example 1, so the oil phase needs the lower freezingpoint. An additional embodiment of example 1 includes placing the secondplate in a low pressure environment.

Devices that contain fluid need a perimeter seal to hold the fluids inthe device. In the example of electrowetting and electrofluidic displaysand devices, the device active area including features for holding inkthat are coated with hydrophobic materials to prevent ink from stickingto the channel or cavity surface and provide for proper deviceoperation. However, these materials also prevent formation of a goodseal in the seal area and connection to the I/O lines. They generallymust be removed from these areas prior to the first fluid filling.Consequently, the first fluid will preferentially stick to the sealperimeter area if it comes in contact with that area. To prevent havingto clean the ink or first fluid off the non-active device area, duringink filling the ink is applied selectively to the active area surfaceonly. An ink roller or meniscus coater can be used to apply the ink, andany excess ink remaining on the surface can be picked up with anadditional roller, for example.

In the example of display devices, the economics of manufacturingtypically dictate multiple displays are fabricated on a single substrateor first plate 10. Each display has its own perimeter, and eachperimeter needs to remain clear of the ink in order to facilitatebonding of the plates (i.e., the top plate 18 to the substrate 10). Atool can be used to fill ink preferentially into the device active areaswhich contain multiple heads, therein applying ink preferentially toeach device area. The top plate 18 can also contain multiple displays,wherein the step of bonding the top plate 18 to the bottom plate 10creates an X-Y array of connected modules. Scribes are made on the firstplate 10 and the second plate 18 to allow the individual displays to beseparated from one another into individual modules. The displays arethen processed as individual display modules for the remaining steps.

In example 1, the substrate 10 was placed into vacuum for ink filling.In the case where the surface features are predominantly wells or holeswith an aspect ratio of 1:1 or higher, and the surface is veryhydrophobic, so simply drawing a meniscus across the surface asdescribed by Jackman et al. (Anal. Chem 1998,70,2280-2287) will not fillthe holes. Instead, a meniscus skin will remain above the well features.Eventually, the meniscus skin will break, thereby leaving just a traceof ink in the well.

In order to get the ink into the well with an aspect ratio of 1:1 orhigher, the foregoing process applies positive pressure to the ink topush the ink into the well. One method of providing this positivepressure is to cover the surface with ink under vacuum (1 to 10 torr)and then increase the pressure (50 torr to atmospheric pressure forexample) before moving the meniscus off the surface, as was done inexample 1. This pressure change forces the ink into the wells allowingthe ink to cleave off when the meniscus slides over the wells. Butpositive pressure can also be applied in the form of a roller or airjet. The ink cleavage may be enhanced with pulsation, changes in thedistance of the meniscus and the surface, and electrical force, asnon-limiting examples.

In contrast to example 1, example 2 provides an alternative method ofink filling of wells when the wells have an aspect ratio nominally lessthan 1:1, while eliminating air bubbles. As an initial step, the ink isoutgassed prior to being loaded into a dispensing device. Referring toFIG. 5A, the ink is dosed into cavities in a substrate 30 under ambientpressure (i.e. in air or N₂) using rollers soaked in ink. In thisexample, there are 90 displays on a large sheet of glass in a 9×10array. A set of 10 rollers positioned precisely over the active areas ofeach device selectively coat ink on the active areas (one roller 32 isshown). The speed of the first plate 30 and the rollers is important forcleaving the ink and providing 100% fill of all the features in eachactive area. Many factors affect the optimal speed but an exemplarynonlimiting range is 5 mm per second to 25 mm per second. The firstsubstrate 30 is positioned with the surface features to be filled facingdown to allow contact by the ink-filled soft, spongy roller 32. Thebottom ends of the roller 32 is in contact with a bath of ink 34,providing a fresh ink supply 36. Ink is applied to the surface of thesubstrate, with excess ink being removed from the surface thereafter.The ink removal cleaves the ink on the surface, but retains the inkwithin the cavities 38 (i.e., wells). It should be noted that the inkevaporates over time in ambient conditions and this may result in thecavities becoming insufficiently filled with ink before a subsequentstep. To address this potential issue, the substrate having the wellsfilled with ink is chilled subsequent to ink filling and prior tosubsequent steps. FIG. 5B shows a series of wells 38 filled with inkusing the roller method.

As shown in FIGS. 6A-6C, an adhesive 40 (e.g., a UV-curable adhesive) isapplied to a top plate 42 (or topstrate), in an exemplary 90 repeatedpatterns in a matrix, and is then aligned and contacts the substrate 44.Pressure is applied to the topstrate-substrate ensemble 46 while theadhesive is UV-cured. A cavity exists between the plates, formedtypically by spacer structures fabricated on a plate. The topplate-substrate ensemble plate stack 46, containing the 90 displays isscribed on both sides and broken into 90 separate display modules 48.These display modules 48 are then positioned face to face to form anexemplary stack of 90 display modules. The cavities of each displaymodule will be filled with a second fluid (oil) in the next step. Theadhesive pattern leaves at least one open port for the later filling ofthe second fluid.

Referring to FIGS. 7A-7C, a stack of modules 50 is placed into a vacuumchamber 12 and air is at least partly pumped out of the channel. Thestack of modules is then dunked into a volume of oil 52 at or near thefreezing point of the ink (first fluid) with the open port 54 at thetop. The ink in the modules is frozen (or becomes extremely viscousprior to the oil fill). The pressure is reduced below 10 torr, andpreferably below 1 torr to fully evacuate the channel. The stack ofmodules is then immersed to allow oil to occupy the (air-free) cavities.An increase in chamber pressure to near atmospheric pressure of an inertgas drives the oil into the channel. The oil does not displace thechilled ink, thereby providing a uniform filling. The stack of modules50 is thereafter removed from the fill chamber and placed under clampingpressure to squeeze the plates together. Excess oil is cleaned from thefill port and a second amount of adhesive seals the fill port.

Referring to FIGS. 8A-8C, a third example also includes a process fordosing two fluids while eliminating air bubbles. As an initial matter,an adhesive 56 (e.g., a UV-curable adhesive) is applied to a top plate58, which is then aligned and contacted to a substrate or first plate60. Pressure is applied to the plates while the adhesive 56 is UV-curedto create a plate stack, which, in FIG. 8A is also a single module 62. Aplurality of cavities exist between the plates in the stack, formedtypically by spacer structures interposing the plates. The foregoingadhesive step results in at least two fill ports 64 in the sealperimeter, generally on opposing sides of each device. Thereafter, afirst fluid 66 (e.g., an ink) completely fills the cavities. Suitablemethods to fill the cavities with ink include placing ink at one fillport and reducing the pressure at the other to draw the ink into thecavities. In the next step, the second fluid 68 (e.g., an oil) isflushed into the cavities, shearing the ink off at the edges of thesurface features in the first plate. The oil will wick through thedevice via capillary wetting and will generally remove all ink unlessthe ink has high viscosity compared to the oil. The resulting device isthen placed under clamping pressure (nominally 3 to 15 psig) to squeezethe module plates together. The pressure sets the proper cell gap byforcing the plates onto the spacer, and pressure can be used to adjustthe tension in the plate stack (module) after the final seal. Withpressure applied, excess ink is cleaned from the fill port and a secondamount of adhesive seals the fill port.

Referring to FIGS. 9A-9C, an electrofluidic device 70 is fabricated bydosing a series of ink droplets 72 with precisely measured volumes ontoa first layer 74, where the ink droplets each have similar volume. Anadhesive (e.g., a W-curable adhesive) is applied to a top plate 76, andthe middle layer 78 is assembled to the top plate 76 by means offixture, adhesive, or the like, which is then aligned and contacted withthe first plate 74 so that the first plate 74 and top plate 76 sandwichthe middle layer 78 therebetween. Pressure is applied to the stack 80while the adhesive is W-cured to form a module 70. A cavity existsbetween the plates of the module, formed typically by spacer structuresfabricated on a plate. The cavity will be filled with a second fluid(oil) in the next step. The adhesive pattern leaves at least one openport for the later filling of the second fluid. The module is placedinto a vacuum chamber 12 and at least some air is pumped out of thechannel. The module 70 is then immersed in oil at or near the freezingpoint of the ink (first fluid) with the open port 82 at the top to abovethe oil level. When the ink is cool, additional air is pumped out of thechannel in suing a chamber pressure of less than 10 torr, and morepreferably less than 1 torr. The module is then fully submersed in oil,and the chamber pressure in increased to drive the oil into the channel.The oil does not displace the chilled ink, providing a uniform filling.The module is removed from the oil fill chamber and placed underclamping pressure to squeeze the plates 70 together. Excess oil iscleaned from the fill port 82 and a second amount of adhesive seals thefill port.

In an alternative process to example 4, a series of multiple displays onthe first plate can be filled with ink using a droplet approach. Afterassembly with a second plate, which includes top plates with areas formultiple displays, the stack plate assembly is scribed on both sides andbroken into individual display modules. The individual display modulesare dosed with oil as in example 4.

Referencing FIGS. 10A-10C, a fifth exemplary process for dosing fluidinto an electrofluidic device utilizes a measured-drop oil fillsequence. Initially, ink 14 is dosed into cavities in a substrate 84 byplacing the substrate 84 in a vacuum chamber 12, pulling a vacuum toremove air from the cavities, ink 14 is applied to the surface as shownin FIG. 10A, and the ink is then removed from the surface. The removalcleaves the ink on the surface and it remains in a cavity. In thisexample, the removal of the ink from the substrate 84 is performed atatmospheric pressure. The ink is chilled to freeze it into the firstsurface structures. Thereafter, an adhesive 86 (e.g., a UVcurableadhesive) is applied to the first plate 84. Measured droplet volumes ofthe second fluid 88 (i.e. oil) are then applied to the second plate 90.The droplets 88 on the second plate 90 have a low surface energy andspread uniformly across the surface. The second plate 90 is cooled toincrease the viscosity of the second fluid 88. Subsequently, the firstand second plates 84, 90 are then aligned and contacted to thesubstrate. Pressure is applied to the stack of the first and secondplates 84, 90 while the adhesive 86 is UV-cured. The second fluid 88 instep 2 has been measured to fill the cavity between the plates. The highviscosities of the first and second fluid prevent the oil from poppingthe ink out of the wells as soon as contact is made. In a preferredembodiment, the oil volume is slightly larger than needed, and a port isleft in the seal area to allow excess oil to squeeze out. The fill portis then cleaned while the plate stack is still under clamping pressure,and adhesive is applied to the port. The adhesive 86 is then cured tocomplete the final seal.

Referring to FIGS. 11A-11C, a sixth exemplary process for dosing fluidsto form an electrofluidic device includes using an emulsion. A firstplate 92 and a second plate 94 are assembled together forming aplurality of cavities there between, with at least one fill port 96 percavity. The plates are scribed on each side and broken apart to yield aplurality of individual modules 98, each with one cavity. The emulsionis introduced into the cavity with a vacuum fill process 100. The module98 undergoes a final seal process where pressure is applied to themodule 98 and the fill port is sealed off. The emulsion 102 is thencollapsed with the application of ultraviolet light, and the polar fluidpreferentially fills the well feature. In additional embodiments, theemulsion can be collapsed with other triggers: thermal, electrical, orother light wavelengths.

This has been a description the present invention, along with thepreferred method of practicing the present invention, however, theinvention itself should only be defined by the appended claims, whereinwe claim:

What is claimed is:
 1. A method for manufacturing an electrofluidic(electrowetting) device comprising the steps of : providing a firstplate with features for holding a first fluid, filling a first fluidinto features on a first plate; providing a second plate; sealing asecond plate onto the first plate forming stacked plates with at leastone cavity between the plates, and leaving at least one fill port for asecond fluid; cooling the stacked plates to increase the viscosity ofthe first fluid so that the first fluid maintains a fixed position as asecond fluid is filled into the cavity; and, filling a second fluid intothe cavity.
 2. The method claimed in claim 1, wherein the features onfirst plate are isolated reservoirs and the features on first plate arefilled by fluid cleavage of the first fluid.
 3. The method claimed inclaim 2, wherein the surface of the first plate is covered with a lowsurface tension material providing for the first fluid to sheet off thesurface cleanly while the fluid remains in the cleaved in the features.4. The method claimed in claim 3, wherein the surface tension of thefirst plate surface in air is less than 25 milliNewtons/meter.
 5. Themethod claimed in claim 2, wherein the step of filling the featuresincludes pumping the air out of the first plate environment and thenbringing the first plate into contact with the first fluid.
 6. Themethod claimed in claim 5, wherein the step of filling the featuresincludes increasing the pressure in the region wherein the first fluidcovers the surface of the first plate and then drawing the fluid overthe surface to cleave the first fluid into the said features.
 7. Themethod claimed in claim 1, wherein the step of filling the first fluidincludes applying the first fluid to the surface with an apparatus thatdrags a first fluid meniscus across the surface.
 8. The method claimedin claim 1, wherein the step of filling the first fluid includesapplying the first fluid to the surface with a rolling apparatus.
 9. Themethod claimed in claim 1, wherein the step of filling the first fluidincludes outgassing the first fluid.
 10. The method claimed in claim 1,wherein the step of filling the first fluid includes cooling the firstfluid to reduce the vapor pressure to the point that less than 5% of thesolvent evaporates between the step of filling the first fluid and thestep of filling the second fluid.
 11. The method claimed in claim 1,wherein the step of sealing a second plate to the first plate includesapplying pressure to the stacked plates to bring the plate surfaces intointimate contact while forming the perimeter bonds.
 12. The methodclaimed in claim 11, wherein the perimeter bonds are formed by curingadhesive.
 13. The method claimed in claim 11, wherein the perimeterbonds are formed by ultrasonic welding.
 14. The method claimed in claim1, wherein the step of filling of the second fluid includes pumping theair out of the cavity.
 15. The method claimed in claim 1, wherein thestep of filling of the second fluid includes bringing the fill port ofthe evacuated cavity into contact with the second fluid, and thenincreasing the pressure to drive the fluid into the cavity.
 16. Themethod according to claim 1, wherein the step of cooling the first fluidinvolves partially submerging the stacked plates into a cooled secondfluid with the fill port oriented upwards such that the fluid does notreach the fill port, and holding the stacked plates in the fluid toallow the fluid in the plates to reach the target temperature.
 17. Themethod claimed in claim 1, wherein the step of filling of the secondfluid includes bringing the second into contact with one of at least twofill ports, and filling the cavity by wicking (capillary wetting). 18.The method claimed in claim 1, which includes the steps of applyingpressure to the stacked plates after the second fluid is filled to setthe final cell gap, applying adhesive to the fill port, and curing theadhesive.
 19. A method for manufacturing an electrofluidic devicecomprising the steps of: providing a first plate with features for afirst fluid; providing a second plate; sealing the said second plateonto the said first plate forming a stacked plate assembly with at leastone cavity between the plates, and leaving at least one fill port forfluid filling; filling a stable mixture of ink and oil fluids betweenthe plates; and, collapsing the mixture into the constituent fluids withexternal stimuli.
 20. A method for manufacturing an electrofluidicdevice comprising the steps of: providing a first plate with featuresfor a first fluid; providing a second plate; sealing the said secondplate onto the said first plate forming a stacked plate assembly with atleast one cavity between the plates, and leaving at least one fill portfor fluid filling; providing a mixture of ink and oil fluids that isstable for a finite time less than 4 weeks, filling the said mixturebetween the plates; and, allowing the mixture to collapse into theconstituent fluids over time.